The present disclosure relates generally to proximity detecting systems and, more particularly, to a flexible capacitive strip for use in a non-contact obstacle detection system, such as may be implemented in conjunction with a motor vehicle power lift-gate, power operated device, or perimeter system.
Various systems have been devised for detecting obstacles in the path of a moveable panel such as an automotive power window, power sliding door or power hinged door. When an obstacle is detected, forward movement (e.g., closing) of the panel is interrupted and, optionally, the movement of the panel may be thereafter reversed (e.g., opened). These detection systems may generally be characterized as either xe2x80x9ccontactingxe2x80x9d or xe2x80x9cnon-contactingxe2x80x9d. In a contacting system, an obstacle is detected only after some form of physical contact occurs between the panel and the obstacle, and may include devices such as pneumatic/pressure sensitive strips, or possibly sensors responsive to changes in mechanical or electrical loading in the apparatus that moves the panel.
On the other hand, in a non-contacting system, an obstacle is detected before actual contact occurs. One specific type of non-contacting obstacle detection system employs the use of a capacitive element(s) as a proximity sensor(s). Capacitive proximity sensors may include one or more electrical conductors formed along the leading edge of a moveable panel, as well as a capacitance sensitive circuit (e.g., a bridge circuit or an oscillator) coupled to the conductor(s). An obstacle (e.g., a human hand) in proximity to the conductor(s) changes the capacitance of the sensor, and the change is thereafter detected by the capacitive sensitive circuit.
Unfortunately, certain problems may arise in creating an appropriate capacitive proximity sensor having the requisite nominal, steady-state capacitance desired for high-sensitive applications, such as the non-contacting obstacle detecting system described above. First, the nominal capacitance value of a capacitive sensing device is inherently dependent upon (among other parameters) the physical dimensions and relative positions of the capacitor electrodes with respect to one another. More specifically, the degree to which the capacitor electrodes are dimensionally consistent with one another along their length will have an effect upon the characteristics of the device. Given the fact that a sensor could be located upon a contoured surface such as a vehicle pillar, panel or moveable lift-gate, the prospect of forming a reliable, sensitive capacitive proximity sensor can therefore be difficult.
Furthermore, it may also be desirable for the sensor to be located in a xe2x80x9ctightxe2x80x9d area that effectively limits the profile of the sensor, and/or provided in an outdoor setting (such as upon a motor vehicle) that is necessarily exposed to moisture. These variables also have an effect on capacitance and, as such, should be taken into account when designing a high-sensitivity, precision capacitive proximity sensor.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a flexible, capacitive strip for use in a non-contact obstacle detection system. In an exemplary embodiment, the strip includes an elongated body for flexible mounting to a panel along a bottom surface of the elongated body. A first elongated planar conductor is contained within an upper section of the elongated body, and a longitudinal cavity is formed through a central portion of the elongated body, the longitudinal cavity being disposed between the planar conductor and the bottom surface. The first elongated planar conductor forms a first electrode of a sensing capacitor and the longitudinal cavity defines a portion of a dielectric material of the sensing capacitor.
In a preferred embodiment, the first elongated planar conductor is a first electrode of a sensing capacitor coupled to the capacitance detector circuit. The longitudinal cavity comprises a portion of a dielectric material of the sensing capacitor. In addition, the panel comprises a second electrode of the sensing capacitor. The planar conductor is preferably a flexible material, such that a substantially constant distance is maintained between the first elongated planar conductor and the panel. The elongated body is formed by extrusion of an insulating material such as santoprene rubber.